Method and apparatus for translating coupling features of a plug-in unit

ABSTRACT

Embodiments of a plug-in unit for an electrical enclosure are disclosed. The plug-in unit includes at least one stab configured to engage a bus, a stab shaft coupled with a base of the at least one stab, and a stab translation mechanism configured to translate the stab shaft such that the at least one stab translates from a retracted position to an extended position.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/234,057, entitled “Method and Apparatus for Translating CouplingFeatures of a Plug-in Unit,” filed on Sep. 15, 2011, which claimspriority to U.S. Provisional Patent Application No. 61/383,053, entitled“Method and Apparatus for Withdrawing a Motor Control Center Unit withthe Structure Door Closed,” filed on Sep. 15, 2010, the full disclosuresof which are incorporated herein by reference in their entireties forall purposes.

BACKGROUND

Techniques in accordance with present embodiments generally relate tomotor control centers and the like, and, more particularly, to a systemand method for translating coupling features or unit line stabs of aplug-in unit.

A motor control center (MCC) is an enclosure that contains standardmotor control equipment. MCCs can include columns and sections havingplug-in units, or “buckets”, which contain motor controls of the MCC.For example, an MCC plug-in unit may include transformers, variablefrequency drivers, feeder circuit breakers, programmable controllers,and so forth. During operation, MCC plug-in units typically contain alive voltage. Indeed, it is common for an MCC plug-in unit to be coupledto a horizontal bus or a vertical bus within the MCC that distributespower across and within the various columns and sections of the MCC. Forexample, a typical MCC plug-in unit may have line contacts, or “stabs”,that connect to the horizontal or vertical bus, thereby providing powerto the MCC plug-in unit. Removing the presence of live voltage fromtraditional MCC plug-in units (e.g., removing the stabs from thehorizontal or vertical bus) often includes opening the MCC plug-in unitto facilitate manual removal of the stabs from communicative couplingwith the bus.

BRIEF DESCRIPTION

In one embodiment of the present invention, a motor control systemincludes an arc flash resistant enclosure and a plug-in unit disposedwithin the arc flash resistant enclosure. The plug-in unit includes astab assembly having at least one stab and a stab translation mechanismconfigured to translate the at least one stab from a retracted positionto an extended position. The motor control system further includes anactuator configured to activate the stab translation mechanism fromoutside of the arc flash resistant enclosure.

In a second embodiment, a plug-in unit includes at least one stabconfigured to engage a bus, a stab shaft coupled with a base of the atleast one stab, and a stab translation mechanism configured to rotatethe stab shaft such that the at least one stab rotationally transitionsfrom a retracted position to an extended position.

In a third embodiment, a plug-in unit includes a stab assembly having atleast one stab configured to engage a bus and a stab translationmechanism configured to translate the stab assembly between a retractedposition and an extended position. The plug-in unit also includes adisengagement feedback system configured to provide an indication thatthe stab assembly is in the retracted position.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a front view of an embodiment of an electrical enclosurehaving an MCC plug-in unit including a stab assembly having a pluralityof unit line stabs that are rotationally translated from an engaged to adisengaged position in accordance with an embodiment of the presenttechniques;

FIG. 2 is a perspective view of an MCC plug-in unit having a mechanicalstab translation mechanism configured to rotate a stab assembly having ashaft and a plurality of unit line stabs between engaged position anddisengaged positions, illustrating a shutter assembly in a closedposition;

FIG. 2A is a partial perspective view of the MCC plug-in unit of FIG. 2,illustrating the shutter assembly in an open position and the stabassembly in an engaged position;

FIG. 3 is a partial perspective view of an embodiment of an MCC plug-inunit, illustrating the stab assembly in a position where the unit linestabs are disengaged from vertical bus bars;

FIG. 4 is a partial perspective view of an embodiment of the MCC plug-inunit of FIG. 3, illustrating the stab assembly in a position where theunit line stabs are engaged with vertical bus bars;

FIG. 5 is a partial perspective view of an embodiment of a stabtranslation mechanism configured to translate the stab assembly betweena disengaged position and an engaged position;

FIG. 6 is a perspective view of an embodiment of the stab assemblyhaving a stab shaft and a plurality of unit line stabs supported by thestab shaft;

FIG. 7 is a perspective view of an embodiment of the unit line stabshown in FIG. 6;

FIG. 8 is a cross-sectional perspective view of an embodiment of theunit line stab shown in FIG. 6, taken along line 8-8, illustrating theunit line stab secured to the stab shaft with a retaining clip; and

FIG. 9 is a partial cross-sectional perspective view of an embodiment ofa housing and a stab assembly of an MCC plug-in unit, illustrating anelectrical disengagement feedback system.

DETAILED DESCRIPTION

The present disclosure is directed towards a plug-in unit, such as anMCC plug-in unit, having a translation mechanism that translates one ormore unit coupling features (e.g., line stabs) between an engagedposition and a disengaged position. Specifically, in one embodiment, thetranslation mechanism of an MCC plug-in unit translates a stab assemblyto engage and disengage unit line stabs with a plurality of power buslines. In certain embodiments, the stab assembly includes a stab shaftwhich supports the plurality of unit line stabs. For example, thetranslation mechanism may rotate the stab shaft, thereby translating theplurality of unit line stabs from the disengaged position to the engagedposition. Furthermore, the translation mechanism may be remotelyoperated. Remote operation of the translation mechanism enables anoperator to actuate the translation mechanism with the MCC plug-in unitdoor closed, thereby limiting exposure of electrical conductors insidethe MCC plug-in unit and limiting the need to shut down power to theMCC. Similarly, a door of an electrical enclosure housing the MCCplug-in unit may remain closed during actuation of the translationmechanism. Moreover, the MCC plug-in unit and/or the electricalenclosure may be arc flash resistant and configured to contain an arcblast should one occur. The MCC plug-in unit further includes a lockoutmechanism. As described in detail below, the lockout mechanism may havea mechanical operation, an electrical operation, or both. For example,the lockout mechanism, when actuated, may prevent the translationmechanism from translating the unit line stabs from the disengagedposition so the engaged position. Additionally, the lockout mechanismmay provide electrical or mechanical feedback indicating whether theunit line stabs are in the engaged position or the disengaged position.

Turning now to the drawings and referring to FIG. 1, an electricalenclosure 100 is illustrated in which electrical components of varioustypes may be housed and connected via a bus system. The electricalenclosure 100 may be representative of a motor control center (MCC) orother industrial, commercial, or marine electrical system. In general,the electrical enclosure 100 provides a protective shell around variouselectrical components and the bus system. For example, the electricalenclosure 100 may include a shell 102 made of any suitable material,such as heavy gauge sheet metal, reinforced plastic, and so forth. Theshell 102 may include one or more doors that, when opened, enable anoperator to access components within the electrical enclosure 100.Additionally, the shell 102 of the electrical enclosure 100 may be arcflash resistant. That is, the electrical enclosure 100 may be configuredto contain an arc blast, should an arc blast occur. Further, theelectrical enclosure 100 may include devices such as a programmablelogic controller, switches, motor controls, inverters, rectifiers, andso forth disposed along and/or coupled with the bus system.Specifically, in the illustrated embodiment, the electrical enclosure100 includes a wiring bay section 106 positioned between a pair of powerdrive sections 108, 110. The electrical enclosure 100 further includesan MCC plug-in unit 112. The MCC plug-in unit 112 may includetransformers, variable frequency drivers, feeder circuit breakers,programmable controllers, and so forth. As discussed in detail below,the MCC plug-in unit 112 includes a translation mechanism configured totranslate coupling features (i.e., a stab assembly) to engage anddisengage a plurality of unit coupling features (i.e., line stabs) withone or more of the bus bars 114.

In the illustrated embodiment, the bus bars 114 pass along a back wallof the electrical enclosure 100 and through each of the enclosuresections (i.e., the wiring bay section 106 and each of the drivesections 108, 110). In other embodiments, the bus bars 114 may bearranged differently. For example, the bus bars 114 may extendhorizontally along the back of the electrical enclosure 100 in oneembodiment. Further, in the illustrated embodiment, a pair of groundbars 116 also passes horizontally through the enclosure sections. Thebus bars 114 are made of conductive material (e.g., copper or aluminum)for use with the electrical enclosure 100. During operation, the set ofbus bars 114 receives power and transmits the power to variouscomponents within the electrical enclosure 100 via couplings between thebus bars 114 and the various components. For example, the stab assemblyof the MCC plug-in unit 112 engages with the bus bars 114 and transmitsenergy from the bus bars 114 to certain components within the electricalenclosure 100.

The stab assembly of the MCC plug-in unit 112 may be remotely actuatedby an operator. Specifically, in one embodiment, the operator maycontrol the MCC plug-in unit 112 with a control system 118, which iscommunicatively coupled to the MCC plug-in unit 112 and configured toregulate the operation of the MCC plug-in unit 112. The control system118 may be accessible from outside the electrical enclosure 100 via auser interface 120 that enables configuration of the control system 118.Thus, the operator may control the operation of the MCC plug-in unit 112by submitting commands through the user interface 120. For example, theuser interface 120 may include a display and controls such as knobs,dials, buttons, switches, and so forth, to allow the operator to controland provide input to the MCC plug-in unit 112 via the control system118. In certain embodiments, unit line stabs of a stab assembly in theMCC plug-in unit 112 may be withdrawn from the bus bars 114 based oninstructions received from the user interface 120 or another remotecommunication feature. As will be appreciated, the remote operation ofthe MCC plug-in unit 112 (i.e., the retraction of the unit line stabsfrom the bus bars 114) allows the live voltage from the bus bars 114 tobe removed from the MCC plug-in unit 112 without opening the electricalenclosure 100. Consequently, the arc flash resistance of the enclosure100 is maintained during the translation of the stab assembly of the MCCplug-in unit 112. The display of the user interface 120 may also providesystem feedback regarding the MCC plug-in unit 112. In particular,feedback relating to the engagement or the disengagement of the unitline stabs with the bus bars 114 may be provided to the operator throughthe display of the user interface 120. Alternatively, the control system118 may be connected to another user interface remote from theelectrical enclosure 100.

FIG. 2 is a perspective view of an embodiment the MCC plug-in unit 112having a stab assembly 132 configured to engage a plurality of unit linestabs 134 with the bus bars 114. The MCC plug-in unit 112 has anenclosure 140 which at least partially defines the boundaries of MCCplug-in unit 112. The enclosure 140 may be an arc flash resistantenclosure configured to contain an arc blast within the MCC plug-in unit112, should an arc blast occur. As shown, the enclosure 140 of the MCCplug-in unit 112 has a front panel 142. The MCC plug-in unit 112 furtherincludes a back panel, however, in the illustrated embodiment, the backpanel is removed from the MCC plug-in unit 112 to reveal the stabtranslation mechanism within the interior of the MCC plug-in unit. Thelocation of an installed back panel is indicated by reference numeral144. The front panel 142 of the MCC plug-in unit 112 may include a dooror other opening through which the interior of the MCC plug-in unit 112may be accessed. When the MCC plug-in unit 112 is disposed within theelectrical enclosure 100, the back panel 144 of the enclosure 140 facesthe bus bars 114. Additionally, the front panel 142 of the enclosure 140faces the front shell 102 of the electrical enclosure 100.

A housing cover 146 is disposed on the back panel 144 of the enclosure140. For example, the housing cover 146 may be formed from aglass-filled thermoset polyester. The housing cover 146 functions as anenclosure for the stab assembly 132, which includes the plurality ofunit line stabs 134, wherein each of the plurality of unit line stabs134 is configured to engage with one of the bus bars 114. In theillustrated embodiment, the stab assembly 132 is in the disengaged orretracted position and is behind the housing cover 146. Thus, a largeportion of the stab assembly 132 is concealed by the housing cover 146and is not visible in FIG. 2.

The stab assembly 132 is actuated by a stab translation mechanism 148.In the illustrated embodiment, the stab translation mechanism 148 isspring loaded and is manually operated. For example, in the illustratedembodiment, the stab translation mechanism 148 includes a hand crank 150as an actuator. Additionally, the hand crank 150 may be permanentlycoupled to the stab translation mechanism 148 or removable from the stabtranslation mechanism 148. For example, the hand crank 150 may be aT-handle Allen wrench or other hex drive tool. When rotated in adirection 152, the hand crank 150 translates the unit line stabs 134 ofthe stab assembly 132 from a disengaged position to an engaged position.Furthermore, as shown, the hand crank 150 extends through the frontpanel 142 of the MCC plug-in unit 112 and may likewise extend outside ofthe enclosure 100. Consequently, the hand crank 150 may be operated, andthe stab translation mechanism 148 actuated, with a door or otheropening in the front panel 142 or the enclosure 100 closed. In otherembodiments, the stab translation mechanism 148 may include otheractuators configured to translate the unit line stabs 134 of the stabassembly 132. For example, a user interface (e.g., user interface 120)positioned outside of the enclosure 100 may be employed as the actuator.Therefore, the arc flash resistance of the enclosure 140 and/or theenclosure 100 may be maintained during the actuation of the stabtranslation mechanism 148. In other embodiments, the stab translationmechanism 148 may be hydraulically, pneumatically, or electricallyoperated. As mentioned above, in some embodiments, the stab translationmechanism 148 may be coupled to the control system 118 to be remotelyoperated. For example, the stab translation mechanism 148 may beremotely operated over a network coupled to the control system 118 orusing the user interface 120.

The housing cover 146 of the enclosure 140 further includes a shutterassembly 154 configured to prevent the stab assembly 132 and the unitline stabs 134 from making unintentional or undesired contact with thebus bars 114. In the illustrated embodiment, the shutter assembly 154 isin a closed position, thereby physically preventing the stab assembly132 and the unit line stabs 134 from rotating from the disengagedposition to the engaged position. The shutter assembly 154 includes anupper plate 156 and a lower plate 158. Upon actuation of the stabtranslation mechanism 148, the upper plate 156 translates in a direction160, and the lower plate 158 translates in a direction 162.Specifically, the stab translation mechanism 148 is coupled to the upperand lower plates 156 and 158 by a shutter translation plate 164. Whenthe hand crank 150 is rotated in the direction 152, the stab translationmechanism 148 translates the shutter translation plate 164 in adirection 166. As the shutter translation plate 164 moves in thedirection 166, the shutter translation plate 164 engages with the upperand lower plates 156 and 158, causing the upper and lower plates 156 and158 to move in the directions 160 and 162, respectively. In particular,guide pins 167 engaged with tracks 168 formed in the upper and lowerplates 156 and 158 guide the upper and lower plates 156 and 158 in thedirections 160 and 162, respectively. In this manner, the shutterassembly 154 creates apertures through which the unit line stabs 134 ofthe stab assembly 132 pass as the stab assembly 132 is translated fromthe disengaged position to the engaged position. Similarly, when thehand crank 150 is rotated in a direction 246, the shutter assembly 154will translate to the closed position shown. In certain embodiments, theshutter assembly 154 may be part of a disengagement feedback system.Specifically, the shutter assembly 154 may be configured to close anelectrical circuit when the shutter assembly 154 is in the closedposition. For example, the shutter transition plate 164 may beconfigured to contact an electrical contact when the shutter assembly154 is in the closed position, thereby closing an electrical circuit andproviding feedback to a user that the shutter assembly 154 is closed andthe stab assembly 132 is in the disengaged position.

As mentioned above, upon actuation of the stab translation mechanism148, the stab assembly 132 translates the plurality of unit line stabs134 from the disengaged position to the engaged position. In thedisengaged position, the unit line stabs 134 are retracted, and theshutter assembly 154 is in the closed position. As discussed below, inthe engaged position, the shutter assembly 154 is in the open positionand the unit line stabs 134 are extended to facilitate engagement withbus bars (e.g., bus bars 114).

The illustrated embodiment of the MCC plug-in unit 112 further includesa mechanical lockout mechanism 155. A discussed in detail below, whenengaged, the mechanical lockout mechanism 155 physically blocks thetranslation of the stab assembly 132 from the disengaged position to theengaged position. As will be appreciated, the mechanical lockoutmechanism 155 may be engaged to prevent the actuation of the stabassembly 132 during installation or removal of the MCC plug-in unit 112from the electrical enclosure 100. Further, the lockout mechanism 155may provide a visible indication of the status of the stab assembly 132such that an operator can identify whether the stab assembly 132 is inan engaged or a disengaged position.

FIG. 2A is a partial perspective view of the MCC plug-in unit 112,illustrating the shutter assembly 154 in an open position with the stabassembly 132 and the unit line stabs 134 in an engaged position. Asdiscussed above, the shutter assembly 154 is configured to block thestab assembly 132 and the unit line stabs 134 from making unintentionalcontact with the bus bars 114 when the stab assembly 132 is in thedisengaged position. Upon actuation of the stab translation mechanism148, the shutter assembly 154 is translated from a closed position to anopen position. When the shutter assembly 154 is in the open position,apertures 169 are formed. With the apertures 169 formed, the stabassembly 132 and the unit line stabs 134 are able to freely rotate fromthe disengaged position to the engaged position shown.

FIG. 3 is a perspective view of the MCC plug-in unit 112 of FIG. 2 withthe housing cover 146 removed, thereby providing a clear view of ahousing 170 supporting the stab assembly 132. The illustrated embodimentincludes similar elements and element numbers as the embodiment shown inFIG. 2. As discussed in detail below, the stab assembly 132 includes astab shaft 174 which supports the plurality of unit line stabs 134. Asshown, the stab assembly 132 is in the disengaged position. That is, theunit line stabs 134 are retracted from, and do not contact, the bus bars114. More specifically, the unit line stabs 134 are in an uprightposition against the housing 170 of the MCC plug-in unit 112.Furthermore, while the stab assembly 132 is in the disengaged position,the lockout mechanism 155 may be engaged to block the translation of thestab assembly 132 from the disengaged to the engaged position.

The stab assembly 132 shown in the illustrated embodiment has arotational translation configuration. Specifically, when the hand crank150 is rotated in the direction 152, the stab translation mechanism 148will actuate the stab assembly 132. As discussed in detail below, theactuation of the stab assembly 132 causes the stab shaft 174 to rotatein a rotational direction 178. As a result, the unit line stabs 134 ofthe stab assembly 132 are translated in the rotational direction 178from the upright position shown in FIG. 3 (i.e., the disengagedposition) to an extended position (i.e., the engaged position) such thatthe unit line stabs 134 engage or are configured to engage the bus bars114. Specifically, as the unit line stabs 134 rotate in the rotationaldirection 178, each unit line stab 134 engages with a respective bus bar114. As will be appreciated, the rotational translation configuration ofthe stab assembly 132 requires a limited amount of space between theenclosure 140 of the MCC plug-in unit 112 and the bus bars 114. Further,the rotational translation configuration conserves horizontal spacewithin the MCC plug-in unit 112 relative to a linear activation. Inother embodiments, the stab assembly 132 may have other translationconfigurations. For example, the stab assembly 132 may have a lineartranslation configuration.

FIG. 4 is a perspective view of the MCC plug-in unit 112 of FIG. 3 withthe housing cover 146 removed, illustrating the stab assembly 132 in theengaged position. Specifically, the unit line stabs 134 of the stabassembly 132 are engaged with the bus bars 114. The illustratedembodiment includes similar elements and element numbers as theembodiment shown in FIG. 3. As shown, in the engaged position, each unitline stab 134 is engaged with a respective one of the bus bars 114.Specifically, each unit line stab 134 has contact arms 180 which abutthe bus bars 114 when the stab assembly 132 is in the engaged position.Indeed, each unit line stab 134 has two contact arms 180 which receiveand abut a respective bus bar 114 on opposite sides. In otherembodiments, different contact arm arrangements may be utilized. Asmentioned above, power (i.e., live voltage) is transferred from the busbars 114 to the MCC plug-in unit 112 through the unit line stabs 134.The power transferred to the MCC plug-in unit 112 is then transmitted tovarious components within the electrical enclosure 100. While theillustrated embodiment includes three unit line stabs 134, in otherembodiments the MCC plug-in unit 112 may include one or a plurality ofunit line stabs 134.

FIG. 5 is a perspective view of an embodiment of the stab translationmechanism 148 and the stab assembly 132 of FIG. 3. The illustratedembodiment includes similar elements and element numbers as theembodiment shown in FIG. 3. As mentioned above, the stab translationmechanism 148 is spring loaded and is manually operated. Specifically,the stab translation mechanism 148 has a rack and pinion system 200 thatis configured to actuate the stab assembly 132, which has a rotationaltranslation configuration.

As shown, the stab translation mechanism 148 has a frame 202 whichsupports the various components of the stab translation mechanism 148.For example, the frame 202 may be formed or machined from a metal suchas steel or aluminum. In certain embodiments, the frame 202 is securedto the back panel 144 of the MCC plug-in unit 112. As discussed above,the hand crank 150 of the stab translation mechanism 148 is rotated inthe direction 152 to actuate the stab translation mechanism 148.Specifically, the hand crank 150 is coupled to the frame 202 of the stabtranslation mechanism 148 by a shaft 204. The shaft 204 extends from thehand crank 150, through the front panel 142 (not shown) of the MCCplug-in unit 112, and is received by the frame 202. In certainembodiments, the shaft 204 may also extend through the shell 102 of theelectrical enclosure 100. As the hand crank 150 is rotated in thedirection 152, the shaft 204 is also rotated in the direction 152.Additionally, the shaft 204 is coupled to a shaft lever 206, which abutsthe frame 202. More particularly, the shaft lever 206 is disposed on theside of the frame 202 opposite the hand crank 150 and is secured to theshaft lever 206 with a shaft bushing 208. The shaft lever 206 is furthercoupled to a linkage assembly 210 by a guide pin 212. As will beappreciated, the shaft lever 206 and the linkage assembly 210 arecoupled such that the shaft lever 206 and the linkage assembly 210 mayrotate with respect to one another. More particularly, the shaft lever206 and the linkage assembly 210 rotate with respect to one anotherabout the guide pin 212 as the hand crank 150 is rotated in thedirection 152.

In the illustrated embodiment, the linkage assembly 210 is furtherpivotably coupled to a drive plate assembly 214 by a guide pin 216. Thedrive plate assembly 214 is pivotably coupled to the frame 202 of thestab translation mechanism 148 by a drive plate shaft 218. As thelinkage assembly 210 is actuated in response to the turning of the handcrank 150 in the direction 152, the drive plate assembly 214 is rotatedabout the drive plate shaft 218 in a direction 220.

As mentioned above, the stab translation mechanism 148 is spring loaded.Specifically, a spring guide assembly 222 is also pivotably coupled tothe drive plate assembly 214 by a guide pin 224. As shown, a spring 226is axially disposed about the spring guide assembly 222. In particular,the spring 226 abuts retaining ledges 228 of the spring guide assembly222 and a spring seat 230 which is secured to the frame 202 by afastener 232. As shown, the spring guide assembly 222 extends through anaperture in the spring seat 230. In operation, as the drive plateassembly 214 is rotated in the direction 220, the spring guide assembly222 extends through the spring seat 230 in a direction 234. As thespring guide assembly 222 extends through the spring seat 230 in thedirection 234, the spring 226 is compressed between the retaining ledges228 of the spring guide assembly 222 and the spring seat 230.

The stab translation mechanism 148 also includes a rack linkage assembly236 coupled to the drive plate assembly 214. The rack linkage assembly236 is further coupled to a rack slider 238. As mentioned above, thestab translation mechanism 148 includes the rack and pinion system 200.The rack and pinion system 200 includes a rack 240 and pinion 242. Morespecifically, the rack 240 is coupled to the rack slider 238, and thepinion 242 is integrated with the stab shaft 174. In operation, as thedrive plate assembly 214 is actuated in the direction 220 upon theturning of the hand crank 150 in the direction 152, the rack linkageassembly 236 and the rack slider 238 are translated in a direction 244.Consequently, the rack 240 is translated in the direction 244. As therack 240 moves in the direction 244, the rack 240 engages with thepinion 242 of the stab shaft 174 (i.e., teeth in the rack 240 and thepinion 242 engage with one another), thereby initiating rotation of thestab shaft 174 and the stab assembly 132 in the rotational direction178. That is, when the hand crank 150 is turned in the direction 152,the stab translation mechanism 148 actuates the stab assembly 132 in themanner described above, thereby translating the stab assembly 132 fromthe disengaged position to the engaged position. As discussed above,when the stab assembly 132 rotates in the rotational direction 178, theunit line stabs 134 translate from the upright position shown in FIG. 5to the extended position shown in FIG. 4, where the unit line stabs 134contact the bus bars 114.

Just as the hand crank 150 may be rotated in the direction 152 totranslate the stab assembly 132 from the disengaged position to theengaged position, the hand crank 150 may also be rotated in a direction246. When the hand crank 150 is rotated in the direction 246, the stabtranslation mechanism 148 will translate the stab assembly 132 from theengaged position to the disengaged position. Specifically, rotating thehand crank 150 in the direction 246 will cause the unit line stabs 134to rotate from the extended position (i.e., in contact with the bus bars114) shown in FIG. 4 to the upright position shown in FIG. 5.

The stab translation mechanism 148 may also be remotely actuated by thecontrol system 118. Specifically, the stab translation mechanism 148 maybe coupled to the control system 118, which is further coupled to theuser interface 120 or a system network. In embodiments where the stabtranslation mechanism 148 is remotely actuated, an operator may actuatethe stab translation mechanism 148, thereby translating the unit linestabs 134 from the engaged position to the disengaged position, or viceversa, without being proximate to the electrical enclosure 100. As willbe appreciated, remote actuation of the stab translation mechanism 148enables an operator to be shielded from live voltage and a potential arcflash when the unit line stabs 134 engage and disengage with the busbars 114. In particular, remote actuation enables an operator to operatethe stab translation mechanism 148 with the doors of the electricalenclosure 100 closed, or with the operator outside an arc flash boundaryof the electrical enclosure 100.

As mentioned above, the stab translation mechanism 148 includes themechanical lockout mechanism 155. The mechanical lockout mechanism 155may be manually or remotely operated to physically block the actuationof the stab translation mechanism 148. Specifically, in the illustratedembodiment, the mechanical lockout mechanism 155 includes an interlocklever 248 and a lockout linkage 250. The mechanical lockout mechanism155 is operated by translating the lockout linkage 250 in the direction252. As the lockout linkage 250 is translated in the direction 252, theinterlock lever 248, which is coupled to the lockout linkage 250 by afastener 254, is also translated in the direction 252. As the interlocklever 248 is translated in the direction 252, the interlock lever 248engages with a slot 256 in a lockout brace 258. As shown, when theinterlock lever 248 is engaged with the slot 256 in the lockout brace258, the interlock lever 248 blocks the movement of a rack bracket 260coupled to the rack 240 in the direction 244. As a result, the rack 240cannot be translated in the direction 244 to enable rotation of the stabassembly 132, thereby preventing the unit line stabs 134 from beingtranslated from the disengaged position to the engaged positions. Incertain embodiments, the front panel 144 of the MCC plug-in unit 112and/or the shell 102 of the electrical enclosure 100 may include slotsor openings to receive the lockout linkage 250. Such embodiments mayenable the mechanical lockout mechanism 155 to be operated with the MCCplug-in unit 112 and the electrical enclosure 100 closed. For example,the arc flash resistant electrical enclosure 100 may be closed, therebycontaining a potential arc flash within the electrical enclosure 100 orthe MCC plug-in unit 112. With the electrical enclosure 100 closed, themechanical lockout mechanism 155 may be actuated to prevent thetranslation of the stab assembly 132 from the disengaged to the engagedposition (i.e., prevent the unit line stabs 134 from rotating andcontacting the bus bars 114). After the mechanical lockout mechanism 155is actuated and the translation of the stab assembly 132 is blocked, thedoors of the electrical enclosure 100 may be opened and the MCC plug-inunit 112 may be removed or replaced.

FIG. 6 is a perspective view of an embodiment of the stab assembly 132,illustrating the stab shaft 174 and the unit line stabs 134. Asdiscussed in detail below, each unit line stab 134 is coupled to thestab shaft 174 with a retaining clip 270. In the illustrated embodiment,the stab shaft 174 is formed from multiple stab shaft segments 272. Asshown, the stab shaft segments 272 interlock with one another to formthe stab shaft 174. The interlocking configuration of the stab shaftsegments 272 enables the unit line stabs 134 of the stab assembly 132 toself-align with the bus bars 114. More specifically, the stab shaftsegments 272 interlock and may have an adjustable connection 274. Inparticular, the stab shaft segments 272 may shift relative to oneanother in an axial direction 276. For example, as the stab assembly 132is rotated from the disengaged position to the engaged position, and asthe unit line stabs 134 come into contact with the bus bars 114, thestab shaft segments 272 may shift in the axial direction 276 relative toone another, thereby enabling the unit line stabs 134 to self-align withthe respective bus bars 114.

In the illustrated embodiment, each stab shaft segment 272 furtherincludes a unit line stab cavity 278 configured to receive a unit linestab 134. As discussed in detail below, the unit line stab 134 isreceived by the unit line stab cavity 278 of the stab shaft segment 272and secured within the unit line stab cavity 278 with the retaining clip270. Also, as mentioned above, the stab shaft 174 includes the pinion242 of the rack and pinion system 200. Specifically, one of the stabshaft segments 272 is molded or formed to include the pinion 242. Incertain embodiments, the stab shaft segments 272 may be molded from athermoplastic, thereby having a high strength and a high stiffness.Furthermore, stab shaft segments 272 molded from a thermoplastic may bechemical resistant and may be substantially impervious to grease orother lubricants that the stab shaft 174 may contact.

FIG. 7 is a perspective view of an embodiment of the unit line stab 134in accordance with present embodiments. In certain embodiments, the unitline stab 134 is made from an electrically conductive material, such astin-plated copper, to enable the unit line stab 134 to transmitelectricity from the bus bar 114 to the various components within theelectrical enclosure 100. As mentioned above, the unit line stab 134includes contact arms 180 configured to abut the bus bar 114 when thestab assembly 132 is in the engaged position shown in FIG. 4. Thecontact arms 180 are coupled to a base portion 300 that is secured tothe stab shaft segment 272 within the unit line stab cavity 278. Theunit line stab 134 also includes backup springs 302 disposed on an outersurface 304 of the unit line stab 134. Specifically, the backup springs302 are disposed in recesses 306 formed in the contact arms 180 of theunit line stab 134. In operation, the backup springs 302 serve toprovide support to the contact arms 180. Specifically, over time, thecontact arms 180 may become relaxed, which may cause the contact arms180 to not maintain a complete connection with the bus bar 114 when thestab assembly 132 is in the engaged position. The backup springs 306,which may be made of stainless steel, help keep the contact arms 180biased towards a central axis 308 of the unit line stab 134, therebyproviding solid contact between the contact arms 180 and the bus bar 114when the stab assembly 132 is in the engaged position.

Furthermore, the contact arms 180 of the unit line stab 134 have angledcontact prongs 310 configured to receive the bus bar 114 as the stabassembly 132 is translated from the disengaged position to the engagedposition. In particular, the contact prongs 310 are configured toreceive the bus bar 114 when the stab assembly 132 is translated usingmultiple translation configurations. As mentioned above, in certainembodiments, the stab assembly 132 may be configured to rotate the unitline stabs 134 from the disengaged position to the engaged position. Forexample, in the illustrated embodiment, the unit line stab 134 mayrotate in a direction 312 from the disengaged position to the engagedposition. As the unit line stab 134 rotates in the direction 312, thecontact prongs 310 to first contact and receive the bus bar 114 will belower contact prongs 314. As shown, the lower contact prongs 314 areangled outward and downward such that the lower contact prongs 314 willcontact and receive the bus bar 114 as the unit line stab 134 rotates inthe direction 312.

Additionally, the stab assembly 132 may be configured to linearlytranslate from the disengaged position to the engaged position (i.e., ina direction 316). As the unit line stab 134 is translated in a direction316 (i.e., linearly toward the bus bar 114), the lower contact prongs314 and upper contact prongs 318 will contact and receive the bus bar114 at approximately the same time. As a result, the upper and lowercontact prongs 314 and 318 are each angled outward such that the upperand lower contact prongs 314 and 318 will contact and receive the busbar 314 as the unit line stab 134 is linearly translated in thedirection 316.

FIG. 8 is a cross-sectional perspective view of the unit line stab 134secured to the stab shaft segment 272 within unit line stab cavity 278.As mentioned above, the unit line stab 134 is secured to the stab shaftsegment 272 with the retaining clip 270. As shown, the retaining clip270 is disposed between the base portion 300 of the unit line stab 134and a lug stub 330 of the unit line stab 134. Additionally, theretaining clip 270 is received within a recess 332 in the unit line stabcavity 278. As will be appreciated, the retaining clip 270 enables theunit line stab 134 to remain stationary and secure within the unit linestab cavity 278 of the stab shaft segment 272 as the stab assembly 132is translated between the engaged and disengaged positions (i.e., as theunit line stab 134 engages and disengages the bus bar 114).

FIG. 9 is a perspective view of the housing 170 of the stab assembly132, which may be coupled to the back panel 144 of the MCC plug-in unit112. The illustrated embodiment includes an electrical disengagementfeedback system 350 configured to provide feedback to an operatorregarding the position of the stab assembly 132. Specifically, theelectrical disengagement feedback system 350 includes electricalcontacts 352 disposed within the housing 170 of the stab assembly 132.As shown, the electrical disengagement feedback system 350 includes twoelectrical contacts 352 proximate to each unit line stab 134. In certainembodiments, certain electrical contacts 352 are electrically coupled toone another and/or electrically coupled to the control system 118 oranother feedback system. For example, in the illustrated embodiment,electrical contacts 354 and 356 are electrically coupled to the controlsystem 118, electrical contacts 358 and 360 are electrically coupled toone another, and electrical contacts 362 and 364 are electricallycoupled to one another.

In operation, when the stab assembly 132 is in the disengaged positionshown in FIG. 9, the unit line stabs 134 contact the two respectiveelectrical contacts 352 proximate to each unit line stab 134. Morespecifically, each upper contact prong 318 of each unit line stab 134contacts a respective electrical contact 352. When the upper contactprongs 318 contact the respective electrical contact 352, an electriccircuit between the control system 118, the electrical contacts 352 andthe unit line stabs 134 is complete (i.e., closed). When this electricalcircuit is closed, the control system 118 may provide feedback to anoperator that the stab assembly 132 is in the disengaged position (i.e.,the unit line stabs 132 are removed from the bus bars 114). For example,the control system 118 may be configured to alert an operator that thestab assembly 132 is in the disengaged position through a visual oraudible indication on the user interface 120. As will be appreciated,the feedback provided by the control system 118 that the stab assembly132 is in the disengaged position may indicate to an operator that theelectrical enclosure 100 may be opened, as the power from the bus bars114 has been removed from the MCC plug-in unit 112. Similarly, when thestab assembly 132 is not in the disengaged position, the electricalcircuit between the control system 118, the electrical contacts 352 andthe unit line stabs 134 will not be complete (i.e., the electricalcircuit will be open), and the control system 118 may indicate to anoperator that the stab assembly 132 is not in the disengaged position(i.e., power from the bus bars 114 may not be removed from the MCCplug-in unit 112). The electrical disengagement feedback system 350, inaddition to the mechanical lockout mechanism 155, enables an operator toverify that the stab assembly 132 is or is not in the disengagedposition (i.e., that the unit line stabs 134 are removed from the busbars 114).

As discussed above, embodiments of the present disclosure include theMCC plug-in unit 112 having the stab translation mechanism 148configured to translate the stab assembly 132 between disengaged andengaged positions. Specifically, the stab translation mechanism 148 maybe actuated manually or remotely over a network or using the controlsystem 118. Furthermore, the stab translation mechanism 148 may beactuated while the electrical enclosure 100, which may be arc flashresistant, remains closed. With the electrical enclosure 100 closed, thestab translation mechanism 148 may be used to disconnect the stabassembly 132 from the bus bars 114, and any potential arc generated inthe electrical enclosure 100 will be contained by the enclosure 100.Moreover, certain embodiments include the mechanical lockout mechanism155 and/or the electrical disengagement feedback system 350. Inparticular, the mechanical lockout mechanism 155, when engaged,physically blocks the actuation of the stab translation mechanism 148,thereby preventing the translation of the stab assembly 132 from thedisengaged position to the engaged position. Additionally, theelectrical disengagement feedback system 350 provides feedback to anoperator regarding the position of the stab assembly 132. Specifically,the electrical disengagement feedback system 350 may indicate to anoperator if the stab assembly 132 is in the disengaged position (i.e.,with the unit line stabs 134 retracted from the bus bars 114) or theengaged position (i.e., with the unit line stabs 134 in contact with thebus bars 114).

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

The invention claimed is:
 1. A motor control center (MCC) plug-in unit,comprising: a stab shaft comprising a plurality of shaft segmentsconfigured to move relative to one another along an axis of the stabshaft; at least one stab configured to engage a bus, wherein the atleast one stab is coupled to the stab shaft and extends outwardly fromthe stab shaft, wherein the at least one stab comprises: a firstplurality of stab leads, wherein each stab lead of the first pluralityof stab leads is angled outward relative to a central axis of the atleast one stab; a second plurality of stab leads, wherein each stab leadof the second plurality of stab leads is angled outward relative to thecentral axis of the at least one stab; and a stab translation mechanismconfigured to rotate the stab shaft about the axis of the stab shaftsuch that the at least one stab rotationally transitions about the axisof the stab shaft from a retracted position to an extended position;wherein the second plurality of stab leads is configured to contact thebus before the first plurality of stab leads contact the bus when the atleast one stab is rotated from the retracted position to the extendedposition.
 2. The MCC plug-in unit of claim 1, wherein the stab shaftcomprises a plurality of molded components, wherein the plurality ofmolded components are configured to interlock and to allowself-alignment of the at least one stab.
 3. The MCC plug-in unit ofclaim 1, wherein the at least one stab comprises a backup springconfigured to bias arms of the at least one stab toward one another. 4.The MCC plug-in unit of claim 1, wherein the stab translation mechanismis configured to be remotely operated via a control system.
 5. The MCCplug-in unit of claim 1, wherein the stab translation mechanism iselectrically driven, manually driven, or pneumatically driven.
 6. TheMCC plug-in unit of claim 1, wherein each stab lead of the secondplurality of stab leads is angled downward relative to the central axisof the at least one stab when the at least one stab is in the extendedposition.
 7. The MCC plug-in unit of claim 1, wherein the firstplurality of stab leads is above the second plurality of stab leadsrelative to the central axis of the at least one stab.
 8. The MCCplug-in unit of claim 1, comprising a disengagement feedback systemconfigured to provide an indication that the at least one stab is in theretracted position.
 9. The MCC plug-in unit of claim 8, wherein thedisengagement feedback system comprises an electrical feedback system,wherein the electrical feedback system comprises an electrical circuitthat is configured to be closed by contact with the at least one stabwhen the at least one stab is in the retracted position.
 10. The MCCplug-in unit of claim 8, wherein the disengagement feedback systemcomprises a mechanical lockout, where actuation of the mechanicallockout prevents translation of the at least one stab from the retractedposition to the extended position.
 11. The MCC plug-in unit of claim 8,wherein the disengagement feedback system comprises: a shutter assemblyconfigured to close and prevent contact between the at least one staband the bus when the at least one stab is in the retracted position; andan electrical feedback system including an electrical circuit that isconfigured to be closed by contact with the shutter assembly when theshutter assembly is closed.
 12. A motor control center (MCC) plug-inunit, comprising: a stab shaft comprising a plurality of shaft segmentsconfigured to move relative to one another along an axis of the stabshaft; at least one stab configured to engage a bus, wherein the atleast one stab is coupled to the stab shaft and extends outwardly fromthe stab shaft; a stab translation mechanism configured to rotate thestab shaft about the axis of the stab shaft such that the at least onestab rotationally transitions about the axis of the stab shaft from aretracted position to an extended position; and a disengagement feedbacksystem configured to provide an indication that the at least one stab isin the retracted position, wherein the disengagement feedback systemcomprises a shutter assembly configured to close and prevent contactbetween the at least one stab and the bus when the at least one stab isin the retracted position, and wherein the disengagement feedback systemcomprises an electrical feedback system including an electrical circuitthat is configured to be closed by contact with the shutter assemblywhen the shutter assembly is closed.
 13. The MCC plug-in unit of claim12, wherein the disengagement feedback system comprises a mechanicallockout.
 14. The MCC plug-in unit of claim 13, where actuation of themechanical lockout prevents translation of the at least one stab fromthe retracted position to the extended position.